The present invention relates to an optical recording and reproducing apparatus and more particularly to a circuit for assuring the quality of information to be recorded in an optical disk device as such an apparatus.
In an optical disk device in which the read/write of information is performed using a light beam, it is a common technique to detect the amount of light reflected from an optical disk to set the write level of information or detect the dirty state in an optical system and the optical disk due to dust or the like.
Japanese Patent Application JP-A-61-13450 is related to an optical disk device.
In this prior art, the amount of light reflected from the optical disk is detected as a signal in a detector (photo-electric converter), the detected signal is amplified to provide an output voltage and the output level. Then, if the output voltage is lower than a constant level, i.e. the amount of the reflected light is less than a predetermined amount, this fact is provided as detection information to a user of the apparatus.
More specifically, the above prior art is composed of a photo-electric converter, a D.C. amplifier and a comparator. The reflected light form the optical device is converted into current by the detector (e.g. photo-electric converter); the current is amplified by the D.C. amplifier to provide an output voltage corresponding to the light amount of the reflected light; and this output signal is compared with a signal having a predetermined level by the comparator. Then, if the output signal is lower than the signal having the predetermined level, this fact is provided to a user as detection information.
Generally, the level of the detected signal based on the reflected light varies depending on the type of optical system, e.g., optical disk, etc. The above prior art does not take into consideration large variations in the light reflection factor of the optical disk, the light detection sensitivity, the gain of the D.C. amplifier, etc. Therefore, in order that the prior art can assure the quality of the recorded data also in the case where there are the above variations, it is necessary to set the detection level of the reflection light at a considerably high level. Thus, as the case may be, quality of the recorded data will be higher than is necessary and possibly useful media will be excluded.